A first-person shooter (Commonly called FPS) is an action-packed video game that involves an avatar, one or more ranged weapons, and a varying number of enemies. FPS renders the game world from the visual perspective of the player character. It was one of the first genres to use key technologies such as 3D graphics, online play, and modding. Enhanced realism combined with graphic violence has also made FPS a common topic in ongoing controversies over video games.

I have collected some quality free and open source first-person shooter games. From this list, I have only tried ActionCube, which I really had fun playing with. Hence, I would love to try all of these games someday. Just a little warning to parents though; most of these games are really violent so you better let your little kids sleep first before splurging with these.

Now without any more delay, here's my list of free and open source FPS games:

AssaultCubeAssaultCube, formerly ActionCube sets in a realistic looking environment, as far as that´s possible with this engine, while gameplay stays fast and arcade. This game is all about team oriented multiplayer fun. Although, a single player mode exists which consists of computer-controlled bots. It also includes Cube's map maker which allows for in-game editing.

AssaultCube is available for Microsoft Windows, Linux and Mac OS X. While the Cube engine is free software, parts of AssaultCube, such as the graphics, are proprietary.

Cube Cube is an open source multiplayer and singleplayer first person shooter game built on an entirely new and very unconventional engine. Cube is a landscape-style engine that pretends to be an indoor FPS engine, which combines very high precision dynamic occlusion culling with a form of geometric mipmapping on the whole world for dynamic LOD for configurable fps & graphic detail on most machines. Uses OpenGL & SDL.

Most of the engine design is targeted at reaching feature richness through simplicity of structure and brute force, rather than finely tuned complexity.

Aleph OneAleph One (formerly known as the Marathon Open Source Project) is an open-source first-person shooter engine based on the source code of Bungie Studios' Marathon 2: Durandal.

The project commenced in early 2000, when Bungie released the code shortly before being acquired by Microsoft and spurred the fan community to further develop it. Since that time, Aleph One has become a successful project in terms of development and community support. Its name is taken from one of the cardinal numbers (\aleph_1) in mathematics and references Marathon Infinity ("normal" infinity is \aleph_0), the final game in the Marathon Trilogy.

NexuizNexuiz is a 3d deathmatch game project, created online by a team of developers called Alientrap. It is available for download for Windows, Mac, and Linux (all the same archive).The first version was released May 31st 2005, released entirely GPL and free over the net, a first for a project of its kind. Since then it has been downloaded over half a million times, and the game is still being updated and developed, currently at version 2.3 and new releases being developed.

OpenArenaOpenArena is a free and open source 3D computer game that belongs to the "first-person shooter" genre. OpenArena had its first public test release on August 19 2005, the day after the id Tech 3 GPL source code release and also the last day of Quake Expo 2005.

OpenArena is being developed using mainly free and open source software. For instance, its game engine is id Software's GPL id Tech 3. OpenArena is entirely free as in speech. The game engine, game code and data are all free and open content.

It is still in very early development. In addition, a "missionpack" add-on is planned, to take advantage of the GPL'd Quake III: Team Arena source code.

Tremulous Tremulous blends a team based FPS with elements of an RTS. Players can choose from 2 unique races, aliens and humans. Players on both teams are able to build working structures in-game like an RTS. These structures provide many functions, the most important being spawning. The designated builders must ensure there are spawn structures or other players will not be able to rejoin the game after death. Other structures provide automated base defense (to some degree), healing functions and much more...

Player advancement is different depending on which team you are on. As a human, players are rewarded with credits for each alien kill. These credits may be used to purchase new weapons and upgrades from the "Armoury". The alien team advances quite differently. Upon killing a human foe, the alien is able to evolve into a new class. The more kills gained the more powerful the classes available.

The overall objective behind Tremulous is to eliminate the opposing team. This is achieved by not only killing the opposing players but also removing their ability to respawn by destroying their spawn structures.

WarsowWar§ow or Warsow, often abbreviated as W§W or WSW, is a multiplayer first-person shooter computer and video game first publicly released on June 8, 2005. The game is actively developed by a crew of freelance software developers and artists. War§ow prides itself on high-quality content standards with thorough testing by selected members of the community.War§ow’s codebase is open source software, distributed under the terms of the GPL; it is built upon Qfusion, an advanced modification of the Quake II engine. The artwork and other media is still copyrighted by its respective authors, although it is free to redistribute in its unmodified form.

War§ow is based on the E-novel Chasseur de bots by Fabrice Demurger. The novel is the basis of the game's cyberpunk visual style, which is achieved by combining cel-shaded cartoon-like graphics with dark, flashy and dirty textures. Since visual clarity is important in maintaining competitive gameplay, War§ow tries to keep effects minimalistic, clear and visible.

SauerbratenSauerbraten (a.k.a. Cube 2) is a free multiplayer/singleplayer first person shooter, built as a major redesign of the Cube FPS.

Much like the original Cube, the aim of this game is not necessarily to produce the most features & eyecandy possible, but rather to allow map/geometry editing to be done dynamically in-game, to create fun gameplay and an elegant engine.

In addition to the FPS game which is in a very playable state, the engine is being used for an RPG which is in the preproduction phase. Additionally, Proper Games ltd are the first to use the engine commercially. dot3 labs is a company started by the creators of Sauerbraten that offers commercial support.

If you know of other free and open source first-person shooter (FPS) games that I failed to include here, you can add them via comment.